Tumor Burden Postsurgery Not Predictive of Survival in mRCC

Roxanne Nelson BSN, RN

November 08, 2015

MIAMI — Cytoreductive nephrectomy has been associated with improvement in overall survival in patients with metastatic renal cell carcinoma (mRCC), a benefit that has been based on the amount of tumor burden removed at the time of surgery.

However, a study that measured the three-dimensional (3D) volume of the primary tumor raises questions about the assumption that most of the tumor needs to be resectable to go ahead with surgery.

Conventional one-dimensional (1D) imaging measurements of the primary tumor's diameter frequently overestimate mRCC primary tumor volume, according to study author Michael L. Blute Jr, MD, a clinical instructor in the Department of Urology at the University of Wisconsin–Madison.

When 3D volumetric measurements were used, higher primary tumor burden was not associated with worse outcomes in patients with mRCC treated with cytoreductive nephrectomy, Dr Blute reported here at the 14th International Kidney Cancer Symposium (IKCS).

"Previous studies have shown improved outcomes with cytoreductive nephrectomy, and they have looked at cross-sectional imaging based on the amount of tumor removed during surgery, generally based on [1D] measurements, assuming that the tumors are perfect spheres," he said.

"Newer imaging processing software has allowed us to measure these tumors in three dimensions," Dr Blute pointed out. "With [3D] volume imaging, measurements are cross-sectional and take into account coronal, sagittal, and axial images."

Thus, image processing has enabled more accurate 3D measurements of tumor volume when compared with volume calculated from 1D measurements. The objective of the current study was to compare 3D volume with 1D volume and to determine whether the measured primary tumor burden is predictive of overall survival after cytoreductive nephrectomy in patients with mRCC.

Dr Blute and colleagues looked at patients with mRCC who had been treated with cytoreductive nephrectomy since 2006. "This is the targeted therapeutic era, and we looked at imaging studies for the primary tumor and all measureable metastatic lesions," he explained.

Tumor Burden Not Associated With Survival

Patients were analyzed by groups based on the primary tumor burden, using either calculated 1D volume or measured 3D volume. Variables were considered continuously and using a cut point of 90% primary burden.

Imaging from all tumor sites was available for 72 patients before undergoing surgery. Within this group, 69% had died of their disease, 32% had grade 4 lesions, and 35% presented with 2 or more metastatic sites.

The researchers found there were no significant differences when stratifying the patients. "We looked at a number of factors, and most importantly, we looked at the percentage of tumor volume removed at the time of surgery to see if it predicted survival," Dr Blute said.

In 14 (19.4%) patients, the 1D volume was within ±10% of the 3D volume. For 51 (70.8%) patients, the primary tumor 1D volume overestimated by more than 10% of the actual 3D volume. This included 13 (18%) patients with 1D volume at least 100% greater than the 3D volume.

For 7 (9.7%) patients, the 1D volume was less than the 3D volume, but neither 3D nor 1D volume of the primary tumor or metastatic sites was associated with overall survival (P = .17 or .08, .99 or .06).

"When we looked at the 90% cut point, when the patient had 90% of the tumor removed, there was no significant association with either 1D or 3D measurement," Dr Blute said.

He pointed out that there was a "loose association with survival in 1D measurement, but keep in mind, this frequently overestimates the true tumor volume."

As a continuous variable, 1D primary tumor burden was associated with overall survival (hazard ratio, 1.02; 95% confidence interval, 1.00 - 1.03; P = .036).

Conversely, the actual 3D primary tumor burden was not associated with overall survival (P = .89).

When measured by 3D imaging, there was no difference in survival based in the actual tumor volume removed. "Stated another way, when a patient in our series had 45% or over 90% removed, the median overall survival was not statistically different," Dr Blute said. "In fact they were almost the same."

Approached for an independent comment by Medscape Medical News, R. Houston Thompson, MD, a professor of urology at the Mayo Clinic, Rochester, Minnesota, noted that the study had "interesting and novel data suggesting that amount of metastatic disease burden was not associated with survival in cytoreductive nephrectomy patients."

"If confirmed by others, these findings may expand the role of cytoreductive nephrectomy for [patients with mRCC], which is currently advocated only when the majority — some use a 75% cut point — of disease can be resected with surgery," Dr Thompson commented.

14th International Kidney Cancer Symposium (IKCS). Presented November 6, 2015.

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